JP3770148B2 - Apparatus and method for exhaust gas purification of internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technology for an exhaust gas purification apparatus for an internal combustion engine, and more particularly to a technology for controlling fuel addition.
[Prior art]
[0002]
In recent years, in an internal combustion engine mounted on an automobile or the like, before the exhaust gas discharged from the internal combustion engine is released into the atmosphere, carbon monoxide (CO), hydrocarbon (HC), nitrogen oxidation contained in the exhaust gas It is required to improve exhaust emission by purifying or removing toxic gas components such as substances (NOx).
[0003]
In particular, in a compression ignition type diesel engine using light oil as fuel, in addition to carbon monoxide (CO), hydrocarbon (HC), nitrogen oxide (NOx), etc., soot contained in exhaust gas, SOF (Solbule It is important to purify or remove particulates called PM (Particulate Matter) such as Organic Fraction.
[0004]
The main component of the fine particles is black smoke (soot) caused by fuel, but it is also a mixture of various components, and the components are insoluble depending on whether they are soluble in organic solvents or not. And the unburned fuel and soluble oil (SOF).
[0005]
Soot is thought to be caused by a complex reaction that occurs when fuel burns in an air-deficient state, but in summary, fuel molecules undergo a dehydrogenation reaction through thermal decomposition, resulting in particulate nuclei (soot precursor). And the nuclei aggregate and coalesce to form soot. In diesel combustion, a large amount of soot is produced during diffusion combustion, but recombustion occurs when air is introduced into the flame at a later stage of combustion, and soot is rapidly reduced. Sulfate is oxidized sulfur of combustion and is in the form of sulfuric acid mist combined with water.
[0006]
For this reason, in a diesel engine, a particulate filter made of a base material with a large number of small pores made of entrained air bubbles and a specific surface area per unit volume increased is arranged in the exhaust passage, and the particulate filter has pores. There is known a method in which fine particles in exhaust gas are adsorbed on the surface and collected by flowing exhaust gas.
[0007]
By the way, if the particulates collected by the particulate filter increase excessively, the exhaust passage in the particulate filter is blocked, and the flow of exhaust gas is hindered.
[0008]
When the flow of exhaust gas is blocked by the particulate filter, the exhaust pressure increases in the exhaust passage upstream of the particulate filter, and the exhaust pressure acts on the internal combustion engine as a back pressure.
[0009]
For this reason, it is necessary to regenerate the particulate filter by purifying the collected fine particles before the fine particles collected by the particulate filter increase excessively.
[0010]
As a method for regenerating the particulate filter, there is a method in which the collected fine particles are oxidized, that is, burned by making the inside of the particulate filter an oxidizing atmosphere.
[0011]
However, since the fine particles are ignited and burned at a high temperature of about 500 ° C. to 700 ° C., in order to oxidize the collected fine particles, the ambient temperature of the particulate filter is raised to a high temperature of 500 ° C. to 700 ° C. In addition, the atmosphere around the particulate filter must be an oxygen-excess atmosphere.
[0012]
However, since a diesel engine performs a lean combustion operation with excess air in most operating regions, the combustion temperature of the air-fuel mixture tends to be low, and the temperature of the exhaust gas tends to be low accordingly. Therefore, in a diesel engine, it is difficult to raise the atmospheric temperature of the particulate filter to 500 ° C. or higher by using the heat of the exhaust gas.
[0013]
On the other hand, a diesel exhaust particle filter as described in Japanese Patent Publication No. 7-106290 has been proposed. The diesel exhaust particle filter described in this publication has a relatively low temperature of about 350 ° C. to 400 ° C. by supporting a catalytic material containing a mixture of a platinum group metal and an alkaline earth metal oxide on a particulate filter. It enables ignition and combustion of fine particles even under temperature conditions.
[0014]
On the other hand, the exhaust gas temperature of the diesel engine may rise to 350 ° C. or higher in the high load operation region, but hardly rises to 350 ° C. or higher in the low load operation region. Therefore, when the diesel engine is operated at a low load, particularly when the fuel injection is stopped, such as when the diesel engine is in a decelerating operation state, low temperature exhaust gas is discharged from the diesel engine. It is assumed that the filter is cooled by the low temperature exhaust gas, and the particulate oxidation ability of the particulate filter is reduced.
[0015]
Therefore, in order to oxidize the fine particles on the particulate filter during low load operation, it is necessary to raise the temperature of the particulate filter to a temperature at which the fine particles can be oxidized at a minimum.
[0016]
As one of means for raising the temperature of the particulate filter, means for adding fuel on the particulate and raising the particulate filter bed temperature by heat released when the fuel is oxidized to oxidize and burn the particulates. There is.
[0017]
There are the following methods for supplying the fuel for raising the particulate filter bed temperature. A part of the fuel injected into the engine cylinder as a power source is not burned into the exhaust gas by performing a secondary fuel injection after the combustion process of the injected fuel normally performed in the cylinder is completed. There are a method in which unburned fuel is included and discharged and added to the exhaust passage, and a method in which a fuel injection device is provided in the exhaust passage and fuel is directly injected into the exhaust gas and added.
[0018]
[Problems to be solved by the invention]
The method of adding as unburned fuel in the cylinder is that the added fuel is sufficiently vaporized. Since the fuel is sufficiently vaporized by being sprayed in the form of a mist in a high-temperature combustion chamber, the combustion reactivity on the particulate filter is improved. It is possible to react even in the vicinity of the minimum temperature at which reaction is possible.
[0019]
Also, if the temperature distribution of the particulate filter is uneven, only the downstream side reaches the reaction temperature, and the upstream side does not reach the reaction temperature, and if it is vaporized fuel, it will pass through the upstream side and on the downstream side. As a result, it becomes possible to raise the temperature of the entire particulate filter to a temperature at which reaction is possible.
[0020]
However, the method of adding as unburned fuel in the cylinder uses a part of the fuel converted to motive power for the reaction, so the absolute amount thereof is limited, and the engine is in a high load state. However, there is a problem that it may be impossible to supply unburned fuel in consideration of torque reduction.
[0021]
On the other hand, in the method of injecting and adding fuel into the exhaust passage, the fuel is supplied and injected in a system different from the system for supplying fuel to the cylinders in the engine, so the injection amount is also increased. It is possible to add fuel without being restricted by the operating state of the engine.
[0022]
However, in the method of adding fuel by injecting it into the exhaust passage, liquid fuel is injected in the form of a mist, so in order to change this into a gas state that is easy to react, the injected fuel can be changed in a short time. In order to enable vaporization, the exhaust gas temperature at the injection position of the exhaust passage needs to be high to some extent. Since the added fuel is not completely gas, when reacting on the particulate filter, the particulate filter bed temperature is deprived as latent heat when the fuel changes from liquid to gas. Therefore, this particulate filter bed temperature also needs to be higher than the minimum temperature required for the reaction. In addition, there is fuel that adheres to the exhaust pipe around the injection location during fuel injection, so if the exhaust pipe temperature is low, it accumulates as a liquid, especially when it is injected at a trap-shaped location such as a collecting pipe (manifold). There are problems such as the need for countermeasures.
[0023]
The present invention has been made in view of the above-mentioned problems. Fine particles deposited on the particulate filter by adopting an efficient fuel addition method based on various conditions of the internal combustion engine and the exhaust system are collected. The problem is to remove.
[0024]
[Means for Solving the Problems]
In order to solve the above problems, a filter provided in the exhaust passage of the internal combustion engine for collecting particulates in the exhaust gas and a main fuel injection for power conversion performed in the combustion chamber of the internal combustion engine are separately provided. In the exhaust purification apparatus, comprising: a combustion chamber fuel addition means for performing secondary fuel injection for injecting fuel; and an exhaust passage fuel addition means for injecting fuel into the exhaust gas provided in the exhaust passage. When the secondary fuel injection is possible in the chamber and the filter bed temperature is equal to or higher than the first temperature at which the gaseous fuel is oxidized, the fuel is added by the fuel addition means in the combustion chamber, and the exhaust gas When the temperature is equal to or higher than the second temperature that does not condense the fuel injected in the exhaust passage, and the filter bed temperature is equal to or higher than the third temperature that causes oxidation reaction of gaseous fuel containing droplets, By means of fuel addition in the passage Thus, an exhaust gas purification apparatus for an internal combustion engine is provided.
[0025]
The present invention selectively uses a secondary fuel injection in the combustion chamber and a fuel injection in the exhaust passage according to the temperature conditions of the engine peripheral elements that change according to the operating conditions of the internal combustion engine. In this case, fuel is added.
[0026]
This means that the internal combustion engine is in a low-load state and secondary fuel injection is possible in the combustion chamber, and the filter bed temperature condition is that the filter bed temperature is equal to or higher than a predetermined temperature. If all of the above are satisfied, fuel is added to the filter by performing secondary fuel injection in the combustion chamber. In addition, if the conditions of the exhaust passage in which fuel can be injected in the exhaust passage when the temperature of the exhaust passage is equal to or higher than a certain temperature and the filter floor temperature condition that the filter floor temperature is equal to or higher than a predetermined temperature, the exhaust passage Fuel is added to the filter by injecting fuel therein.
[0027]
Further, when both of the condition settings that determine the two means are satisfied, that is, secondary fuel injection is possible in the combustion chamber, and the filter bed temperature is used to oxidize the gaseous fuel. 1 is higher than each of the third temperatures at which the gaseous fuel containing droplets undergoes an oxidation reaction, and the exhaust passage temperature is equal to or higher than the second temperature at which the fuel injected in the exhaust passage is not condensed. The fuel is added using one or both of the fuel adding means in the combustion chamber and the fuel adding means in the exhaust passage.
[0028]
In performing the fuel addition means for both the fuel addition in the combustion chamber and the fuel addition in the exhaust passage, each fuel addition means has a condition for the filter bed temperature. The first temperature as a condition is a minimum temperature at which the gaseous fuel can be oxidized on the filter. The third temperature, which is the condition of the filter bed temperature of the fuel addition means in the exhaust passage, is the same as that on the filter even if the latent heat necessary for the gaseous fuel containing droplets to become a complete gas is deprived on the filter. This is the minimum temperature at which the fuel can react. Accordingly, the third temperature is higher than the first temperature because the fuel has latent heat for transferring to the gas.
[0029]
The fuel addition to the filter by the fuel addition means in the combustion chamber on the condition of the first temperature is added to the filter with the fuel that has been injected into the combustion chamber in a high temperature state and is completely vaporized, so that the reactivity is high. It becomes good. Therefore, it is possible to cause a temperature rising reaction even at the first temperature which is a low temperature region, but the addition of fuel to the filter by fuel injection in the exhaust passage on the condition of the third temperature causes the liquid to be atomized. After injection, the fuel is vaporized by the injection position atmosphere and fuel is added to the filter. Therefore, depending on the surrounding atmosphere, not all of the injected fuel is vaporized, so that the fuel addition is performed at a third temperature that is a certain high temperature range.
[0030]
In relation to the first and third temperatures, the second temperature, which is the exhaust temperature, is a temperature at which the fuel injected into the exhaust passage does not condense, that is, when fuel is added to the exhaust passage. It is a temperature at which the fuel added to can be kept so as not to accumulate in the exhaust passage as a liquid.
[0031]
The filter retains nitrogen oxides in the exhaust gas when the oxygen concentration in the exhaust gas is high, and reduces the retained nitrogen oxides when the oxygen concentration decreases and fuel as a reducing agent is present. An NOx storage reduction catalyst can be supported.
[0032]
In addition to the above characteristics, the NOx storage reduction catalyst activates oxygen in the exhaust gas when the oxygen concentration in the exhaust gas is high, decreases the oxygen concentration, and nitrogen exists when fuel as a reducing agent is present. While reducing the oxide, it also generates active oxygen. Therefore, this active oxygen is used to purify nitrogen oxides in the exhaust gas, and at the same time, serves as an oxidant when burning fine particles.
[0033]
By carrying out the present invention, it is possible to efficiently remove the fine particles deposited on the particulate filter according to various conditions of the internal combustion engine and the exhaust system.
DETAILED DESCRIPTION OF THE INVENTION
[0034]
Hereinafter, an embodiment in which a fuel injection control device and method for an internal combustion engine according to the present invention is applied to a diesel engine system will be described.
[0035]
In FIG. 1, an internal combustion engine (hereinafter referred to as an engine) 1 is an in-line four-cylinder diesel engine system having a fuel supply system 10, a combustion chamber 20, an intake system 30, an exhaust system 40, and the like as main parts.
[0036]
The fuel supply system 10 includes a supply pump 11, a pressure accumulation chamber (common rail) 12, a fuel injection valve 13, a cutoff valve 14, a fuel addition nozzle 17, an engine fuel passage P1, an addition fuel passage P2, and the like.
[0037]
The supply pump 11 increases the pressure of the fuel pumped up from the fuel tank (not shown) and supplies it to the common rail 12 through the engine fuel passage P1. The common rail 12 has a function of holding (accumulating) high-pressure fuel supplied from the supply pump 11 at a predetermined pressure, and distributes the accumulated fuel to each fuel injection valve 13. The fuel injection valve 13 is an electromagnetic valve provided with an electromagnetic solenoid (not shown) therein, and is appropriately opened to supply and inject fuel into the combustion chamber 20.
[0038]
On the other hand, the supply pump 11 supplies a part of the fuel pumped up from the fuel tank to the fuel addition nozzle 17 via the added fuel passage P2. A shutoff valve 14 is disposed in the fuel passage P2 from the supply pump 11 toward the fuel addition nozzle 17. In an emergency, the shutoff valve 14 shuts off the added fuel passage P2 and stops the fuel supply. The fuel addition nozzle 17 is an electromagnetic valve similar to the fuel injection valve 13 and is a fuel addition means in the exhaust passage according to the present invention that injects and adds fuel as a reducing agent into the exhaust system 40.
[0039]
The intake system 30 forms a passage (intake passage) for intake air supplied into each combustion chamber 20. On the other hand, the exhaust system 40 forms a passage (exhaust passage) for exhaust gas discharged from each combustion chamber 20.
[0040]
The engine 1 is provided with a known supercharger (turbocharger) 50. The turbocharger 50 includes a turbine wheel 52 and a compressor 53 that are connected via a shaft 51. One compressor 53 is exposed to the intake air in the intake system 30, and the other turbine wheel 52 is exposed to the exhaust gas in the exhaust system 40. The turbocharger 50 having such a configuration has an effect of increasing the intake pressure (supercharging effect) by rotating the compressor 53 using the exhaust flow (exhaust pressure) received by the turbine wheel 52.
[0041]
In the intake system 30, an intercooler 31 provided in the turbocharger 50 forcibly cools the intake air whose temperature has been raised by supercharging. The throttle valve 32 provided further downstream than the intercooler 31 is an electronically controlled on-off valve whose opening degree can be adjusted in a stepless manner, and restricts the flow passage area of the intake passage under predetermined conditions. The function of adjusting (reducing) the supply amount of the intake air is provided.
[0042]
Further, an exhaust gas circulation passage (EGR passage) 60 that bypasses the upstream (intake system 30) and the downstream (exhaust system 40) of the combustion chamber 20 is formed in the engine 1. Specifically, the EGR passage 60 communicates the exhaust collecting pipe 40 a upstream of the turbocharger 50 in the exhaust system 40 and the downstream side of the throttle valve 32 in the intake system 30. The EGR passage 60 has a function of returning a part of the exhaust gas to the intake system 30 as appropriate. The EGR passage 60 is opened and closed steplessly by electronic control, and an EGR valve 61 that can freely adjust an exhaust flow rate flowing through the passage, and an exhaust gas that passes through (circulates) the EGR passage 60 is cooled. EGR cooler 62 is provided.
[0043]
Further, in the exhaust system 40, an exhaust passage 40b along the exhaust gas flow path is provided downstream of the exhaust collecting pipe 40a connected from the combustion chamber and a portion where the turbine wheel 52 is provided, and a NOx catalyst casing 42 is provided downstream thereof. Further, the exhaust passage 40c is sequentially connected further downstream. As will be described later, the NOx catalyst casing 42 includes a NOx storage reduction catalyst 42b that purifies harmful components such as NOx contained in the exhaust gas, and particulates (PM) such as soot contained in the exhaust gas, such as NOx. A particulate filter 42a for purification along with harmful components is accommodated (see FIG. 3).
[0044]
Further, various sensors are attached to each part of the engine 1, and signals related to the environmental conditions of the part and the operating state of the engine 1 are output.
[0045]
That is, the rail pressure sensor 70 outputs a detection signal corresponding to the fuel pressure stored in the common rail 12. The fuel pressure sensor 71 outputs a detection signal corresponding to the pressure (fuel pressure) Pg of the fuel introduced into the fuel addition nozzle 17 among the fuel flowing through the added fuel passage P2. The air flow meter 72 outputs a detection signal corresponding to the flow rate (intake amount) Ga of intake air upstream of the throttle valve 32 in the intake system 30. The air-fuel ratio (A / F) sensor 73 outputs a detection signal that continuously changes in accordance with the oxygen concentration in the exhaust gas upstream of the catalyst casing 42 of the exhaust system 40. Similarly, the exhaust temperature sensor 74 outputs a detection signal corresponding to the temperature (exhaust temperature) TEX of the exhaust gas downstream of the catalyst casing 42 of the exhaust system 40. Similarly, the NOx sensor 75 outputs a detection signal that continuously changes in accordance with the NOx concentration in the exhaust gas downstream of the catalyst casing 42 of the exhaust system 40. The catalyst inflow exhaust gas temperature sensor 78 outputs a detection signal corresponding to the temperature of the exhaust gas flowing in at the catalyst casing 42 inlet. The catalyst temperature sensor 79 outputs a detection signal corresponding to the catalyst bed temperature in the catalyst casing 42. The pressure sensor 90 is provided upstream of the catalyst casing 42 and outputs a detection signal corresponding to the pressure in the exhaust passage.
[0046]
The accelerator opening sensor 76 is attached to an accelerator pedal (not shown) of the engine 1 and outputs a detection signal that is a basis of a work amount required in the engine 1 in accordance with the depression amount ACC of the pedal. The crank angle sensor 77 outputs a detection signal (pulse) every time the output shaft (crankshaft) of the engine 1 rotates by a certain angle. These sensors 70 to 79 and 90 are electrically connected to an electronic control unit (ECU) 80.
[0047]
As shown in FIG. 2, the ECU 80 includes a central processing unit (CPU) 81, a read only memory (ROM) 82, a random access memory (RAM) 83, a backup RAM 84 in which stored information is not erased even after the operation is stopped, and a timer counter 85. , An external input circuit 86 including an A / D converter, and an external output circuit 87 are provided with a logical operation circuit configured by being connected by a bidirectional bus 88.
[0048]
The ECU 80 inputs detection signals from the various sensors via an external input circuit, and based on these signals, the CPU 81 included in the ECU 80 performs basic control on the fuel injection of the engine 1 from the program stored in the ROM 82. In addition to the control, various controls related to the operating state of the engine 1 such as determination of the supply amount of the fuel injection related to the addition of the reducing agent (fuel that functions as the reducing agent) and the reducing agent (fuel) addition control related to the addition timing and the like are performed.
[0049]
The fuel supply system 10 for supplying fuel to each cylinder through the fuel injection valve 13, the NOx catalyst and particulate filter provided in the exhaust system 40, and the functions of the fuel supply unit 10 and the NOx catalyst and particulate filter are controlled. The ECU 80 and the like that together constitute an exhaust purification device for the engine 1 according to the present embodiment. The fuel addition control and the like are performed through the operation of various members constituting the exhaust gas purification apparatus, including the ECU 80 that outputs a command signal related to the control.
[0050]
Next, among the components of the engine 1 described above, the configuration and functions of the catalyst casing 42 provided in the exhaust system 40 will be described in detail.
[0051]
FIG. 3 is an enlarged sectional view of the catalyst casing 42 shown in FIG. 1 together with a part of its internal structure. The catalyst casing 42 accommodates therein a particulate filter 42a carrying an NOx storage reduction catalyst 42b.
[0052]
The NOx catalyst 42b is, for example, alumina (AL ₂ O _Three ) As a main material, and functions as a NOx absorbent on the surface of the carrier. For example, alkali metals such as potassium (K), sodium (Na), lithium (Li), and cesium (Cs), barium (Ba ), An alkaline earth metal such as calcium (Ca), or a rare earth such as yttrium (Y), and a noble metal such as platinum (Pt) that functions as an oxidation catalyst (noble metal catalyst) is supported. Consists of.
[0053]
The particulate filter 42a is formed of a porous material such as cordierite, for example. Therefore, the exhaust gas that has flowed into the exhaust inflow passage is surrounded by a porous material as indicated by an arrow because the end is closed. It flows through the partition wall made of a material and flows into the adjacent exhaust inflow passage.
[0054]
In the present embodiment, a carrier layer made of alumina or the like is formed on the surface of the partition wall of the particulate filter 42a and on the inner wall surface of the pores of the partition wall. A NOx catalyst 42b made of NOx absorbent is supported.
[0055]
The NOx absorbent has a characteristic of retaining NOx when the oxygen concentration in the exhaust gas is high and releasing NOx when the oxygen concentration in the exhaust gas is low. Further, when NOx is released into the exhaust gas, if HC, CO, or the like is present in the exhaust gas, the noble metal catalyst promotes an oxidation reaction of these HC and CO, thereby converting NOx into an oxidizing component, HC, A redox reaction using CO as a reducing component occurs between the two. That is, HC and CO are CO ₂ And H ₂ Oxidized to O, NOx is N ₂ Reduced to
[0056]
Further, the noble metal catalyst constituting the NOx catalyst 42b promotes the oxidation of HC and raises the bed temperature by the heat of oxidation reaction of HC.
[0057]
Further, even when the NOx absorbent has a high oxygen concentration in the exhaust gas, if it retains a predetermined limit amount of NOx, it will no longer hold NOx. In the engine 1, before the NOx retention amount of the NOx catalyst 42b accommodated in the catalyst casing 42 reaches a limit, the NOx catalyst 42b is activated by adding and supplying a reducing agent upstream of the catalyst casing 42 in the exhaust passage. The control of reducing and purifying the held NOx and restoring the NOx holding ability of the NOx catalyst 42b is repeated at a predetermined interval.
[0058]
In the particulate filter 42a, as described above, the NOx catalyst 42b supported on the surface of the particulate filter 42a repeatedly holds and reduces and purifies NOx. On the other hand, the NOx catalyst 42b has such NOx. It has the characteristic of raising the temperature in the course of purification and generating active oxygen as a secondary. When exhaust gas passes through the particulate filter 42a, PM components such as soot contained in the exhaust gas are captured by the porous material. Here, since the active oxygen generated by the NOx catalyst 42b has extremely high reactivity (activity) as an oxidant, the trapped PM component emits this active oxygen and luminous flame in a state where the temperature is increased by the addition of fuel. It reacts quickly without being purified.
[0059]
The NOx purification will be specifically described below.
[0060]
In general, in a diesel engine, the oxygen concentration of a mixture of fuel and air used for combustion in a combustion chamber is in a high concentration state in most operating regions. The oxygen concentration of the mixture used for combustion is usually reflected in the oxygen concentration in the exhaust gas as it is after subtracting the oxygen used for combustion, and the oxygen concentration (air-fuel ratio) in the mixture is high. For example, the oxygen concentration (air-fuel ratio) in the exhaust gas basically increases similarly.
[0061]
On the other hand, as described above, the NOx catalyst 42b holds NOx if the oxygen concentration in the exhaust gas is high, and NOx if the oxygen concentration is low. ₂ Or, since it has a characteristic of reducing to NO, as long as the oxygen in the exhaust gas has a high concentration, it keeps holding NOx. However, there is a limit in the amount of NOx retained by the NOx catalyst 42b. When the NOx catalyst 42b retains the limit amount of NOx, NOx in the exhaust gas is not retained by the NOx catalyst 42b and the catalyst casing 42 is Go through.
[0062]
In order to restore the NOx retention action of the NOx catalyst, it is necessary to add a reducing agent to the NOx absorbent. However, due to the engine configuration, when normal fuel injection is performed, the oxygen concentration is low, that is, the reducing agent is used. Exhaust gas containing a large amount of fuel is difficult to exhaust.
[0063]
Therefore, in addition to the main fuel injection for power conversion performed in the combustion chamber of the internal combustion engine, a method of performing secondary fuel injection that mainly injects fuel as unburned fuel, or provided in the exhaust passage, The fuel is added to the exhaust gas by a method of injecting the fuel into the exhaust gas to increase the amount of the reducing agent component in the exhaust gas, and the NOx holding action is restored by this reducing component.
[0064]
The ECU 80 of the engine 1 continuously observes the NOx concentration in the exhaust gas downstream of the NOx catalyst 42b based on the output signal of the NOx sensor 75. The NOx retention capability (retention efficiency) by the NOx catalyst 42b is such that the NOx amount retained by the NOx catalyst 42b increases, that is, the NOx amount retained by the NOx catalyst 42b retains the NOx catalyst 42b. The closer to the maximum amount (saturation amount) of NOx to be obtained, the lower the value. In other words, if the amount of NOx retained in the NOx catalyst 42b increases, the concentration of NOx that passes through the catalyst casing 42 and is discharged downstream also increases. Since these two transition modes have a sufficient correlation, the amount of NOx retained in the NOx catalyst 42b can be grasped based on the transition mode of the NOx concentration.
[0065]
Therefore, when the NOx concentration downstream of the catalyst casing 42 exceeds a predetermined concentration, the ECU 80 determines that the amount of NOx retained in the NOx catalyst 42b has reached a predetermined amount, and uses the fuel addition means to increase the NOx concentration in the exhaust gas. By adding unburned fuel to the exhaust system 40, the fuel is added to the upstream of the catalyst casing 42 of the exhaust system 40, the amount of reducing components in the exhaust gas flowing into the catalyst casing 42 is temporarily increased, and the air-fuel ratio is lowered. Thus, NOx in the catalyst is purified by reacting with fuel as a reducing agent.
[0066]
Next, purification of fine particles (hereinafter referred to as PM) contained in the exhaust gas will be described.
[0067]
Similar to NOx purification, PM is also purified using fuel. However, NOx purification is performed using a chemical reaction between HC and NOx, which are the main components of fuel, whereas PM is purified. In the purification, the temperature is raised mainly using HC as a heat source, and PM and oxygen (O ₂ ) Is activated, oxidized and purified.
[0068]
Therefore, regarding the purification of PM, the added fuel is used as a heat source in the particulate filter 42a, that is, the purification is performed based on the combustion reactivity of the fuel.
[0069]
The main control methods include an operation history in which output signals of the accelerator opening sensor 76, the crank angle sensor 77, the timer counter 85, etc. are stored on the backup RAM 84, and a signal from the pressure sensor 90 installed in the exhaust passage. The CPU 81 determines whether or not to perform fuel addition as a purification method as compared with the program stored in the ROM 82.
[0070]
As for the fuel addition method, as in the case of fuel addition in the NOx catalyst 42b, as shown in FIG. 4, part of the main fuel injection for power conversion performed in the combustion chamber of the internal combustion engine is injected after the combustion process. As shown in FIG. 5, a fuel injection device is provided in the exhaust passage so that the fuel is directly injected into the exhaust gas. There is a method of injecting (fuel addition means in the exhaust passage). Since each of the above methods has different characteristics, these characteristics are also a factor of the judgment material.
[0071]
The characteristics of the fuel adding means in the combustion chamber and the fuel adding means in the exhaust passage will be described below.
[0072]
For fuel addition means in the combustion chamber,
(1) Since fuel is injected into the combustion chamber, it must be sufficiently vaporized by the heat in the combustion chamber.
(2) Since the vaporized and activated fuel flows into the catalyst casing 42, the catalyst bed temperature is the first temperature (minimum temperature at which the vaporized and activated fuel can react) (Assuming about 200 ° C)
(3) The injection amount depends on the fuel amount required from the accelerator pedal depression amount, and the injection amount cannot be changed directly, and the amount is not large.
(4) When the engine is heavily loaded, or when secondary fuel injection is performed at the time of starting the engine, a torque step or the like occurs in the engine.
Etc.
[0073]
Regarding fuel addition means in the exhaust passage,
(1) Since it is injected into the exhaust passage, if the internal temperature of the exhaust passage is not higher than the second temperature (assuming about 300 ° C.), there is a possibility that it will not vaporize and adhere to the inner surface of the exhaust passage to form a liquid pool. thing,
(2) Since all of the injected fuel does not vaporize and may flow into the catalyst casing 42 in a droplet state, it is necessary for the fuel that is a gas containing droplets to become a complete gas on the filter. Even if it takes latent heat, it is not less than a third temperature (assuming about 250 ° C.) that is a minimum temperature at which fuel can react on the filter and is higher than the first temperature,
(3) Because the fuel injection is performed separately from the fuel system added to the engine, the injection amount can be directly controlled without being affected by the operation of the engine, and the amount can be increased.
Etc.
[0074]
In summary, the fuel addition means in the combustion chamber can be added even if the catalyst bed temperature is low, but it depends on the operating condition of the engine, and the injection amount is not so much, and the injection amount can be adjusted. It is difficult. Regarding the fuel addition means in the exhaust passage, the injection amount can be adjusted regardless of the operating condition of the engine, but the catalyst bed temperature needs to be somewhat high, and the exhaust passage temperature is also restricted. Become.
[0075]
Considering the above conditions, a program for determining whether or not fuel can be added will be described. First, when it is determined that PM needs to be accumulated and removed, the temperature of the catalyst outgas is measured by the temperature sensor 74. Here, the catalyst outgas temperature is measured when the catalyst casing 42 is on the high temperature side (≧ 700 ° C.), and the temperature is further increased by adding the fuel, and as a result, the NOx catalyst 42b is thermally deteriorated. Prevention is the main purpose.
[0076]
Next, the possibility of fuel addition in the combustion chamber will be described. After measuring the catalyst exhaust gas temperature, the accelerator opening sensor 76 and the crank angle sensor 77 determine whether the load on the engine 1 is large and measure the engine coolant temperature from a water temperature gauge (not shown). Here, the water temperature is measured because the rotation is unstable immediately after the engine 1 is started, and fuel cannot be added in this state. Therefore, it is determined whether or not the warm-up operation is finished after the engine 1 is started. The engine cooling water temperature was adopted as one of the materials. Next, the catalyst bed temperature is measured by the catalyst bed temperature sensor 79. If the temperature is equal to or higher than a predetermined first temperature (200 ° C.), fuel is added in the combustion chamber.
[0077]
Next, the possibility of fuel addition in the exhaust passage will be described. Similarly, after measuring the catalyst outlet gas temperature, the catalyst inflow exhaust gas temperature sensor 78 measures the catalyst inlet gas temperature. Originally, it is desirable to measure the temperature at the fuel injection position. However, the temperature at the catalyst injection gas is measured from problems such as sensor placement, and the temperature at the fuel injection position is estimated from the measured value. If the catalyst inlet gas temperature is equal to or higher than the predetermined second temperature (300 ° C.), then the catalyst bed temperature is measured by the catalyst bed temperature sensor 79, and if it is equal to or higher than the predetermined third temperature (250 ° C.), exhaust is performed. Fuel addition is performed in the passage, and fuel addition control for PM regeneration is completed.
[0078]
Hereinafter, with respect to “fuel addition control” performed by the ECU 80 of the engine 1 according to the present embodiment, a specific processing procedure will be described with reference to a flowchart shown in FIG. 6.
[0079]
FIG. 6 shows the processing contents of the “particulate filter PM regeneration routine” that is executed to control the fuel addition method and amount required for regeneration when performing PM regeneration control. The routine processing is started simultaneously with the start of the engine 1 through the ECU 80.
[0080]
When the processing shifts to this routine, the ECU 80 determines whether or not PM regeneration is necessary in step S101, an operation history obtained from accumulation of data such as the accelerator opening sensor 76, the crank angle sensor 77, the timer counter 85, and the pressure sensor. 90, it is determined whether regeneration control is necessary, and if it is determined that it is not necessary, the routine proceeds to S112, and normal combustion is performed in S113 without adding fuel in the combustion chamber and fuel in the exhaust passage. Exit the routine and proceed to the next step if necessary.
[0081]
Next, in S102, the status of the catalyst casing 42 is determined from the catalyst outgas temperature. Here, if the output gas temperature ≧ 700 ° C., the routine proceeds to S112, the normal combustion is performed in S113 without adding the fuel in the combustion chamber and the fuel in the exhaust passage, and this routine is terminated. In the case of 700 ° C., it proceeds to the next step.
[0082]
Next, in S103 and after, it is determined whether or not fuel addition in the combustion chamber can be performed. First, in S103, the coolant temperature of the engine 1 is measured. If the water temperature <60 ° C., the process proceeds to S107, without adding fuel in the combustion chamber, and then proceeds to S108, and if the water temperature ≧ 60 ° C., the process proceeds to the next step.
[0083]
Next, in S104, the engine load state is determined. If the load is high, the process proceeds to S107, and without adding fuel in the combustion chamber, the process proceeds to S108. If the load is low, the process proceeds to the next step.
[0084]
Next, in S105, the catalyst bed temperature is measured. If the catalyst bed temperature <200 ° C., the process proceeds to S107 without adding fuel in the combustion chamber, and then proceeds to S108. If the catalyst bed temperature ≧ 200 ° C., the process proceeds to S106, and fuel addition in the combustion chamber is performed, and then the process proceeds to S108.
[0085]
Next, in S108 and after, it is determined whether or not the fuel addition means in the exhaust passage can be performed. First, in S108, the catalyst input gas temperature is measured. If the inlet gas temperature <300 ° C., the routine proceeds to S111, and this routine is terminated without adding fuel in the exhaust passage. If the inlet gas temperature ≧ 300 ° C., the routine proceeds to the next step.
[0086]
In the next S109, the catalyst bed temperature is measured. If the catalyst bed temperature <250 ° C., the routine proceeds to S111 and the routine is terminated without adding fuel in the exhaust passage. If the catalyst bed temperature ≧ 250 ° C., the routine proceeds to S110 and fuel is added to the exhaust passage and then this routine is terminated. To do.
[0087]
In this routine, the possibility of fuel addition in the combustion chamber was discussed, and then the possibility of fuel addition in the exhaust passage was discussed. However, these two fuel additions are performed independently and are essentially in a parallel relationship. However, for the convenience of processing, as described above, fuel in the combustion chamber is first added, and then fuel in the exhaust passage is added. Therefore, conversely, whether or not fuel can be added to the exhaust passage is discussed first, and then whether or not fuel is added to the combustion chamber is discussed, there is no difference in actual control.
[0088]
In the present embodiment, a predetermined temperature is set under each condition, but in actuality, it is not limited to this value, and there is a unique value in each internal combustion engine and exhaust system, and it shall be based on that value. Further, in the step of the routine S108, the catalyst inlet gas temperature is used as the determination condition. As described above, this is one means for estimating the temperature of the fuel injection position in the exhaust passage, and other means such as water temperature, The temperature may be estimated by calculating from the intake air temperature, the injection amount, the rotation speed, and the like. The point is that any means can be used if the temperature at the fuel injection position can be estimated. This also applies to other condition settings. For example, in steps S103 and S104, the water temperature and the engine load state are discussed. This is a condition setting for determining whether or not the engine can perform secondary injection. S103 and S104 are just one means for representing it.
[0089]
In addition, under the condition where both the fuel addition in the combustion chamber and the fuel addition in the exhaust passage can be performed, both fuel additions may be performed, or only one of them may be performed. For example, even when the temperature condition of the exhaust system is sufficient to add fuel in the exhaust passage, it is necessary to add only fuel in the combustion chamber and add fuel in the exhaust passage if the engine is idling. On the contrary, when the engine is operated so as to alternately repeat a high load state and a low load state, the fuel in the exhaust passage is only added without adding fuel in the combustion chamber at the low load. It is possible to regenerate PM.
【The invention's effect】
[0090]
In the exhaust gas purification apparatus for an internal combustion engine according to the present invention, when raising the temperature of a particulate filter having a function of oxidizing PM in exhaust gas, the PM is efficiently converted according to various conditions of the internal combustion engine and the exhaust system. Fuel can be added for more accurate removal.
[0091]
That is, instability when PM is burned on the particulate filter by selecting a fuel addition method for regeneration of PM suitable for the operating condition of the internal combustion engine and the temperature property of the exhaust system, And PM can be burned without causing deterioration of exhaust gas components passing through the catalyst casing and clogging of the catalyst casing with the added fuel.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing a diesel engine system according to an embodiment of the present invention.
FIG. 2 is a conceptual diagram of a configuration around an ECU according to the embodiment.
FIG. 3 is a conceptual cross-sectional view of a catalyst casing according to the same embodiment.
FIG. 4 is a schematic cross-sectional view of an engine and an exhaust system showing fuel addition in the combustion chamber according to the same embodiment.
FIG. 5 is a schematic cross-sectional view of an engine and an exhaust system showing fuel addition in a fuel exhaust passage according to the same embodiment.
FIG. 6 is a flowchart showing PM regeneration control according to the embodiment;
[Explanation of symbols]
1 engine (internal combustion engine)
10 Fuel supply system
11 Supply pump
12 Common rail (accumulation chamber)
13 Fuel injection valve
14 Control valve
17 Fuel addition nozzle
20 Combustion chamber
30 Intake system
31 Intercooler
32 Throttle valve
40 Exhaust system
40a Exhaust collecting pipe
40b, c Exhaust passage
42 Catalyst casing
42a Particulate filter
42b NOx storage reduction catalyst (NOx catalyst)
42c plugging
43 Injection fuel pool
50 turbocharger
51 shaft
52 Turbine wheel
53 Compressor
60 EGR passage
61 EGR valve
62 EGR cooler
70 Rail pressure sensor
71 Combustion sensor
72 Air Flow Meter
73 Air-fuel ratio (A / F) sensor
74 Exhaust temperature sensor
75 NOx sensor
76 Accelerator position sensor
77 Crank angle sensor
78 Catalyst inflow exhaust temperature sensor
80 Electronic control unit (ECU)
81 Central processing unit (CPU)
82 Read-only memory (ROM)
83 Random access memory (RAM)
84 Backup RAM
85 Timer counter
86 External input circuit
87 External output circuit
88 bidirectional bus
90 Pressure sensor
P1 Engine fuel passage
P2 added fuel passage

Claims (7)

A filter provided in the exhaust passage of the internal combustion engine for collecting particulates in the exhaust gas;
Fuel addition means in the combustion chamber for performing secondary fuel injection for injecting fuel separately from the main fuel injection for power conversion performed in the combustion chamber of the internal combustion engine;
In the exhaust emission control device provided in the exhaust passage and provided with fuel addition means in the exhaust passage for injecting fuel into the exhaust gas,
When secondary fuel injection is possible in the combustion chamber and the filter bed temperature is equal to or higher than the first temperature for oxidizing the gaseous fuel, fuel is added by the fuel addition means in the combustion chamber,
When the exhaust gas temperature is equal to or higher than the second temperature that does not condense the fuel injected in the exhaust passage, and the filter bed temperature is equal to or higher than the third temperature that causes oxidation reaction of the gaseous fuel containing droplets, An exhaust emission control device for an internal combustion engine, wherein fuel is added by fuel addition means in the exhaust passage. Secondary fuel injection injection is possible in the combustion chamber, and the filter bed temperature is from a first temperature at which gaseous fuel is oxidized and a third temperature at which gaseous fuel containing droplets is oxidized. When the exhaust passage temperature is higher than a second temperature at which the fuel injected in the exhaust passage is not condensed, one of the fuel addition means in the combustion chamber and the fuel addition means in the exhaust passage; 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein fuel is added using both of them. The first temperature which is the filter bed temperature is a temperature of 200 ° C. or higher at which gaseous fuel can be oxidized, and the third temperature is 250 ° C. or higher at which gaseous fuel containing droplets can be oxidized. 3. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the temperature is a temperature and the third temperature is higher than the first temperature. 4. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 3, wherein the second temperature which is the exhaust gas temperature is a temperature of 300 ° C or higher at which the fuel injected into the exhaust passage does not condense. . When the oxygen concentration in the exhaust gas is high, the filter retains nitrogen oxides in the exhaust gas,
5. The storage reduction type NOx catalyst for reducing the nitrogen oxide held when the oxygen concentration is reduced and the fuel as the reducing agent is present is supported. 6. An exhaust purification device for an internal combustion engine. In addition to the main injection fuel for power conversion performed in the combustion chamber of the internal combustion engine, secondary fuel is injected into a filter provided in the exhaust passage of the internal combustion engine for collecting particulates in the exhaust gas. A first method of adding;
In an exhaust purification method of adding fuel by appropriately selecting a second method of adding fuel by directly injecting fuel into the exhaust gas in the exhaust passage,
Adopting the first method of adding the unburned fuel if the secondary fuel injection is possible in the combustion chamber and the filter bed temperature is equal to or higher than the temperature at which the gaseous fuel can be oxidized.
If the exhaust gas temperature in the exhaust passage is equal to or higher than the temperature at which the fuel injected into the exhaust passage does not condense, and the filter bed temperature is equal to or higher than the temperature at which gaseous fuel containing droplets can be oxidized. An exhaust purification method adopting the second method of directly adding fuel. The secondary fuel injection is possible in the combustion chamber, and the filter bed temperature is higher than the temperature at which the gaseous fuel can be oxidized and the temperature at which the gaseous fuel containing droplets can be oxidized, If the exhaust gas temperature in the exhaust passage is equal to or higher than the temperature at which the fuel injected into the exhaust passage does not condense, either the first method of adding the unburned fuel or the second method of adding the direct fuel The exhaust gas purification method according to claim 6, wherein both are employed.

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